Definition of Transpiration and the factors effecting the rate of transpiration:

What is transpiration?

    • Transpiration is the loss of water vapor through the stomata of leaves.
    • Transpiration occurs mainly through the stomata present in lower epidermis.
    • Stomata are the openings present on the lower epidermis of a leaf. It is also dispersed among the epidermal cell present to the upper epidermis.
    • Stomata has two guard cell that are bean shaped that control the opening and closing of the stomata according to the requirement of water loss.

Different types of Transpiration in plants:

There are three types of transpiration occurs in plants:

    • Stomatal Transpiration: transpiration through stomata.
    • Lenticular Transpiration: transpiration through lenticels present in woody stems and fruits.
    • Cuticular Transpiration: transpiration through cuticle.

Factors affecting the rate of Transpiration:

Humidity:

Transpiration becomes slower in humid conditions. Diffusion of water vapour out of the leaf slows down if the leaf is already surrounded by moist air. It means that higher the concentration of water molecules outside the leaf gradual and gentle the concentration gradient for diffusion.

Wind:

Transpiration is faster in windy conditions. Water vapour is removed quickly by air movement, speeding up diffusion of more water vapour out of the leaf. As the wind blows, it carries moisture from the surrounding of a leaf, making diffusion gradient steeper.

In still air, the water vapour that diffuses out of the leaf makes the air around the leaf more humid, this decreases the rate of transpiration.

Light:

Transpiration increases in bright light. The stomata open wide with more or bright light.

While in darkness, the stomata close, so less water is lost from the leaf.

Temperature:

Transpiration is higher or greater at higher temperature.

Surface Area:

More surface area, more stomata are present so higher the rate of transpiration.

Adaptation of marram grass adapted to dry condition:

    • The leaves of marram grass have adapted to dry conditions.
    • The grooves and hairs of the leaves help to trap a layer of still air, thus reducing

Definition of wilting:

    • Wilting is the loss of turgidity of non-woody parts of a plant

Wilting in plants:

    • Wilting in plants occurs due to continuous water loss by transpiration or evaporation through stomata, plant is dehydrated.
    • Water is lost faster than it gained.
    • Cells are plasmolysed or become flaccid.
    • Due to loss of turgor, tissues can no longer support the plant.
    • Any condition by which process of transpiration becomes faster leads to the wilting in plants,g., lack of water, low humidity, high light intensity, high temperature, wind speed.

Mature plants as compared to newly-transplanted seedlings do not wilt more quickly:

    • Mature plants have well developed root system which remain undamaged.
    • Root hairs increases the surface area for the absorption of water.
    • Due to branched roots, enough water uptake occurs and plant cells or tissues remain turgid.
    • Due to deposition of lignin, xylem supports older plants.

Advantages of wilting:

    • Rate of transpiration reduces because of wilting.
    • The surface area of the leaf exposed to sunlight is reduced that causes the guard cells to flaccid and stomata to close. Eventually rate of transpiration reduces.

Disadvantages of wilting:

    • Rate of photosynthesis reduces because water becomes a limiting factor.
    • As stomata also close so entering of carbon dioxide also affected and here carbon dioxide become a limiting factor.

Test yourself:

    • What is a transpiration?
    • What are the factors affecting on the rate of transpiration?
    • What is stomata?
    • What are guard cells?
    • How does the opening and closing of stomata control?
    • What is the shape of the guard cells?
    • Where are the stomata present?
    • What are the different types of transpiration occurring in plants?
    • What is a stomatal transpiration?
    • What is the cuticular transpiration?
    • What is a lenticular transpiration?
    • Explain how the rate of transpiration in plants is affected by decreasing the humidity of the surrounding air.
    • Explain how the rate of transpiration in plants is affected by increasing the temperature of the surrounding air.
    • What is the definition of wilting in plants?
    • What are factors affecting on the wilting of a plant?
    • What is the advantage of wilting in a plant?
    • What is the advantage of wilting in a plant?
    • How does the marram grass adapted to dry condition?
    • Why do the mature plants as compared to newly-transplanted seedlings not wilt more quickly?
    • What do you mean by limiting factor?

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